Optical fiber array

ABSTRACT

An optical fiber array is provided in which an optical fiber tip end is housed in a holding member  2 . The holding member  2  consists of a substrate  3  and a cover plate  5 . The substrate  3  forms a sectional V shaped housing groove (V groove  4 ) for housing the optical fiber  1  on the top face. The substrate  5  covers the top face of the substrate  3 . Then, an adhesive is filled between the substrate  3  and the cover plate  5 , and an optical fiber  1  is fixed in the housing groove. At this time, a distance Y between the substrate  3  and the cover plate  5  is L/6≦Y≦L relevant to a distance L from a contact point between the housed optical fiber  1  and the housing groove to the cover plate  5 . In this manner, even under severer environment, a release of the holding member or the like hardly occurs, and good characteristics are maintained.  
     Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspect is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an optical fiber array having aholding member mounted thereto, and having optical fibers arranged andheld with predetermined intervals.

[0003] More particularly, the present invention relates to a techniqueof preventing release of the holding member.

[0004] 2. Description of Related Art

[0005] Conventionally, a fiber array having optical fibers arrangedtherein and fixed thereto is formed as shown in FIG. 4. In FIG. 4,reference numeral 12 denotes a holding member that consists of asubstrate 13 and a cover plate 15. A plurality of V grooves 14 having aV shaped section (housing grooves) are formed at the substrate, opticalfibers (optical fiber bare portions) 1 are housed in the individual Vgrooves 14, and an adhesive is filled. Then, the cover plate 15 iscovered to pinch the optical fibers 1, and the optical fibers 1 areadhered and fixed into the V grooves 14. In addition, reference numeral1 a denotes covered optical fibers, where a plurality of the opticalfibers 1 a are coupled with each other to form a fiber ribbon 16.

[0006] The holding member 12 is formed by processing a glass plate, forexample, and the V grooves 14 are formed in parallel on a substrate topwhich is ground to a mirror face. In addition, a space between theadjacent V grooves is small so that an adhesive face is widely formed atthe right and left ends of a bundle of the V grooves in order to ensureadhesion between the substrate 13 and the cover plate 15.

[0007] However, the above described fiber array is often placed underoutdoor severe environment. That is, the fiber array is subject to froma high temperature of 60° C. to a low temperature of −40° C., and issubjected to dry environment like a desert and humid high temperatureenvironment. The optical fiber array must maintain constant and propercharacteristics under such severe environment for a long time. However,in the case where the above fiber array is subject to such environmentfor a long time, there has occurred a phenomenon that the substrate 13and the cover plate 15 fixing the optical fibers 1 are released becauseof variation with an elapse of time, and the optical fibers areunreliably fixed.

[0008] In an optical fiber, if an optical axis deviates from apredetermined position, a transmission loss is increased between thisoptical fiber and optical part being connected therewith. Thus, a veryhigh position precision of 0.5 micron or less is required. Therefore, ifthe above release phenomenon occurs, a displacement occurs, resulting indegraded transmission characteristics. In addition, finally, an opticalfiber may slip off from the substrate.

SUMMARY OF THE INVENTION

[0009] The present invention has been made in order to solve theforegoing problem. It is an object of the present invention to providean optical fiber array in which the release of the holding member or thelike hardly occurs even under severe environment, and propercharacteristics are maintained.

[0010] In order to solve the foregoing problem, according to a firstaspect of the present invention, there is provided an optical fiberarray comprising a holding member that consists of a substrate forming asectional V shaped housing groove for housing an optical fiber on a topface and a cover plate covering the top face of the substrate, so as tohouse the tip of the optical fiber there in, with the bare portion ofthe optical fiber fixed in the housing groove by filling an adhesivebetween the substrate and a cover plate so as to fix the optical fiberto the housing groove, wherein a distance between a center axis of thehousing groove that is at an outermost portion and an end of thesubstrate is 5 times or more than the radium of the optical fiber, and adistance Y between the substrate and the cover plate is L/6≦Y≦L relevantto a distance L from a contact point between the housed optical fiberand the housing grove to the cover plate.

[0011] According to a second aspect of the present invention, there isprovided an optical fiber array according to the first aspect, wherein aheight of a site protruding from the substrate of the optical fiberhoused in the housing groove is substantially equal to the distance Ybetween the substrate and the cover plate.

[0012] According to a third aspect of the present invention, there isprovided an optical fiber array according to the first or second aspect,wherein the distance Y between the substrate and the cover plate isL/4≦Y≦L.

[0013] According to a fourth aspect of the present invention, there isprovided an optical fiber array according to any of the first to thirdaspects, wherein the adhesive is epoxy-based.

[0014] According to a fifth aspect of the present invention, there isprovided an optical fiber array according to any of the first to fourthaspects, wherein the width of the cover plate is different from that ofthe substrate.

[0015] According to a sixth aspect of the present invention, there isprovided an optical fiber array according to any of the first to fifthaspects, wherein a placement face for placing a cover portion of theoptical fiber is provided at the rear part of a housing groove formingface, and a step is provided between the housing groove forming face andthe placement face, thereby placing and housing the optical fiber.

[0016] The Inventor has found the following through testing. That is,the above release is caused by a thin adhesive layer between a substrateand a cover plate that spreads to the outside of the outermost portionof a housing groove. Namely, in the case where a circular optical fiberis housed in a V groove, there occurs contraction in curing an adhesivecaused by an adhesive stay portion at the periphery of optical fibers(in the housing groove); there is a difference in thermal expansion ratebetween the adhesive and the substrate or between the adhesive and thecover plate. Alternatively, increasing humidity causes expansion of theadhesive. And the stress concentration of the adhesive in the V groovecaused by these phenomena cannot be sufficiently by the thin adhesivelayer.

[0017] A fiber array is mounted by an adhesive, and is formed in itscomplicated shape. Thus, there exists a variety of stresses such aspartial strong stress or entire stress between the substrate and thecover plate. The partial stress occurs at a resin stay portion such asthe periphery of the fibers in a V groove, as described above. This isbelieved to be due to a mechanism in which the stress of the adhesivestay portion indicated by A shown in FIG. 5 is applied to a portionindicated by B, and if the adhesive layer of this portion is thin, thisstress cannot be absorbed, and a release occurs with the portion of B.

[0018] For example, if a release occurs with a portion such as B, theentire stress is applied to this portion or water invades the releaseportion, whereby such release is further expanded.

[0019] The above construction is provided in response to such action ofadhesive, whereby the adhesive layer can absorb the stressconcentration, and a release is unlikely to occur between the opticalfiber and the substrate or fixed substrate even under severeenvironment. Then proper characteristics can be maintained.

[0020] Additional objects and advantages of the invention will be setforth in the description which follows, and in part will be obvious fromthe description, or may be learned by practice of the invention. Theobjects and advantages of the invention may be realized and obtained bymeans of the instrumentalities and combinations particularly pointed outhereinafter.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0021] The accompanying drawings, which are incorporated in andconstitute a part of the specification, illustrate presently preferredembodiments of the present invention and, together with the generaldescription given above and the detailed description of the preferredembodiments given below, serve to explain the principle of the presentinvention.

[0022]FIG. 1 is an enlarged sectional view of an optical fiber arrayshowing an example according to the preferred embodiments of the presentinvention;

[0023]FIG. 2A to FIG. 2H are photographs for explaining how a fiberarray adhesive portion is changed due to environment testing, where

[0024]FIG. 2A to FIG. 2D each show a construction of the presentinvention,

[0025]FIG. 2E to FIG. 2H each shows a conventional construction;

[0026]FIG. 3 is an illustrative view of a holding member used inenvironment testing shown in FIG. 2;

[0027]FIG. 4 is a perspective view of an optical fiber array;

[0028]FIG. 5 is an enlarged sectional view illustrating one fiberportion shown in FIG. 4:

[0029]FIG. 6A to FIG. 6C each show how is an adhesive layer end of anoptical fiber array, where

[0030]FIG. 6A is a sectional view illustrating the present invention,

[0031]FIG. 6B is a sectional view illustrating another example of thepresent invention, and

[0032]FIG. 6C is a sectional view illustrating a conventional example;and

[0033]FIG. 7A and FIG. 7B show a construction of a V groove rear end ofthe optical fiber array, where

[0034]FIG. 7A is an illustrative side view of essential parts accordingto the present invention, and

[0035]FIG. 7B is an illustrative side view of conventional essentialparts, wherein reference numeral 1 denotes an optical fiber, referencenumeral 2 denotes a holding member, reference numeral 3 denotes asubstrate, reference numeral 3 a denotes a step, reference numeral 4denotes a V groove, reference numeral 5 denotes a cover plate, referencenumeral 6 denotes an adhesive layer, reference numeral 6 a denotes anadhesive, reference code L denotes a distance from a contact pointbetween a V groove and an optical fiber to a cover plate, reference codeM denotes a distance from a center of a housing groove at the outer mostportion of the substrate to a substrate end, reference code P denotes acontact point between a V groove and an optical fiber, and Y denotesthickness of an adhesive layer.

DETAILED DESCRIPTION OF THE EMBODIMENT

[0036] Reference will now be made in detail to the presently preferredembodiments of the invention as illustrated in the accompanyingdrawings, in which like reference numerals designate like orcorresponding parts.

[0037] Hereinafter, preferred embodiments of the present invention willbe described in detail with reference to the accompanying drawings.

[0038]FIG. 1 is an enlarged sectional view of an optical fiber arrayaccording to the present invention, wherein reference numeral 1 denotesan optical fiber (a bare optical fiber), reference numeral 2 denotes aholding member that consists of a substrate 3 and a cover plate 5, a Vgroove 4 is formed at the substrate 3, and an optical fiber 1 is housedin the V groove 4. In addition, an adhesive 6 a is filled at theperiphery of the optical fiber 1 and between the substrate 3 and thecover plate 5. An opening angle of the V groove 4 is 70 degrees, forexample, and the optical fiber 1 is formed to be 62.5 microns in radius,for example.

[0039] The V groove 4 is formed so that a part of the optical fiber 1,being housed therein, is slightly protruded from the upper face of thesubstrate 3, and is formed so that its protrusion length issubstantially equal to thickness of the adhesive layer 6 formed betweenthe substrate 3 and the cover plate 5. In addition, a distance M betweenthe center of the housing groove at the outer most portion of thesubstrate 3 and the substrate end (shown in FIG. 3) is 5 times or moreof the optical fiber radius relevant to the radium R of the opticalfiber 1.

[0040] Then, the thickness Y of this adhesive layer 6 is defined asfollows when a distance L from a contact point P between the V groove 4and the optical fiber 1 to the cover plate 5 is defined as a reference.

L/6≦Y≦L  (Range 1)

[0041] The thickness Y of the adhesive layer 6 is defined in the aboverange, whereby as shown in the test result described later, the adhesivelayer 6 absorbs a stress generated from contraction generated while theadhesive is cured or a difference in thermal expansion rate or expansionrate between the substrate 3 and the cover plate 5 so that constantcharacteristics can be maintained without being released even undersevere environment.

[0042] In addition, from the viewpoint of adhesive, the stress caused bythe adhesive increases particularly with higher Young Modulus of theadhesive. For example, in the case where an epoxy based adhesive isemployed, the Young Modulus is generally high as compared with an acrylbased or silicon based adhesive. Thus, the stress is also increased, andthe adhesive layer structure of the present application is effective. Inparticular, when an epoxy based adhesive of Young Modulus not less than2 kgf/mm² is used, the stress is particularly increased. Thus, theadhesive layer structure of the present application is effective.

[0043] The adhesive used here denotes one which is used for adhering ofat least V groove periphery (adhering and bonding of the bare fiber,cover plate and substrate) In addition, in order for the optical fiber 1to come into reliable two point contact with the inclined face of the Vgroove 4, it is preferable that a realistic contact point is movedupwardly with a margin of about 10 microns from a theoretical contactpoint in consideration of processing precision or measurement precision.In this case, the above (range 1) is (L−10 microns)/6≦Y≦(L−10 microns).

[0044] Table 1 compares changes of the adhesive portion when environmenttest (boiling test) is carried out by a fiber array created by changingthickness Y of the adhesive layer 6, where the fiber array is soaked inboiling water to investigate an occurrence of the release after apredetermined time has elapsed. In the table, ∘ denotes a good state inwhich no release has occurred, Δ denotes a state in which partialrelease has occurred, and X denotes a state in which an extensiverelease has occurred. TABLE 1 Thickness of adhesive layer Boiling time Y15 hr 36 hr 60 hr L/2 ◯ ◯ ◯ Photograph L/4 ◯ ◯ ◯ L/6 ◯ ◯ Δ L/8 X X XPhotograph

[0045]FIG. 2A to FIG. 2H are photographs for explaining how an optionalfiber array adhering portion is changed due to the above environmenttest, wherein FIG. 2A to FIG. 2D are photographs of Y=L/2 shown in Table1, and FIG. 2E to FIG. 2H are photographs of Y=L/8 in a conventionalexample. In addition, the holding member 3 of the optical fiber arraytaken as each of the photographs shown in FIG. 2 is schematically shownin FIG. 3.

[0046]FIG. 3 is a plan view of the holding member. As shown in thefigure, the holding member 2 provided for environment test has threegroups each consisting of eight grooves on substrate 3. An optical fiberarray is formed in such a way that optical fibers 1 are housed in theholding member 2, adhesive is applied, and then, the cover plate 5 isadhered. The protrusion quantity of the optical fiber 1 from thesubstrate is changed by changing the size of V groove so that thethickness Y of the adhesive is set to its desired thickness.

[0047] In FIG. 2, although there is no change after 60-hour boiling inthe left photographs A to D, it is possible to verify that there occursa spot-like pattern on main adhesive faces 8, 8 of the left and right ofthe substrate after 15 hours and on in the right photographs E to H, anda portion in a different state from a state before boiled occurs betweenthe optional fiber groups as well. These sites are where adhesive hasbeen released. From these photographs, in the case where the right side,i.e., the thickness Y of the adhesive layer is L/8, it is found thatrelease has already occurred after 15 hour boiling. That is, when theleft side, i.e., Y is L/2, no release occurs even after 60 hour boiling.

[0048] Thus, from the test result, it can be judged that, as long as adistance between the center axis of the housing groove at the outermostportion and the substrate end is 5 times or more of the optical fiberradius, and the adhesive layer thickness Y is L/6 or more, the releasehardly occurs, and the optical fiber array can be used even under severeenvironment. Further, if the adhesive layer thickness Y is L/4 or more,it can be judged that no release occurs, and a good state can becontinuously maintained.

[0049] In the meantime, the optical fiber array is generally formed sothat the fibers are pressed in the substrate V groove 4 by the coverplate 5. Although optical grinding is applied to the tip end face of theoptical fiber array, the fiber end face is required to be set to adesired angle. Thus, in general, grinding is performed when a side faceparallel to the V groove 4 is defined as a reference during grinding. Atthis time, although the side face of the substrate 3 can be easilyprocessed so as to be parallel to the V groove 4, the cover plate 5 ismerely loaded on the optical fibers 1. Thus, it is not easy that theside face of the cover plate 5 is parallel to the optical fibers 1.

[0050] Therefore, it is natural that the grinding standard face is onthe side face of the substrate 3 so that the cover plate 5 should not beat the outside of the right and left of the substrate 3 in order toensure this state. As a measure, the width of the cover plate 5 is madesmaller than that of the substrate 3, whereby slight displacement can bepermitted, thus making it possible to apply the cover.

[0051] In this case, as shown in FIG. 6 that is the sectional viewillustrating the optical fiber array, the adhesive 6 a is pooled at astepped portion C in a meniscus manner, which provides an effect ofincreasing adhesive force. However, in the case where the adhesive layeris thin, the stress caused here results in an occurrence of release (themechanism in which a release occurs is similar to that in V groove). Inparticular, this site is situated at the outside, and is subjected toopen air. Thus, if a release occurs, it permits moisture to easilyinvade, which accelerates the progress of release.

[0052] In this manner, this site is an important portion that prevents arelease. As shown in FIG. 1, as long as a large adhesive layer isensured, the stress does not concentrate, and a release hardly occurs.Thus, the construction according to the present invention can ensurehigh reliability in the same way as the V groove portion. FIG. 6A is asectional view illustrating an optical fiber array according to thepresent invention, and FIG. 6C is a sectional view illustrating aconventional optical fiber array.

[0053] As shown in FIG. 6B, even if the width of the cover plate isgreater than that of the substrate, a meniscus-like pool portion isformed at the stepped portion C. The construction of the presentinvention, i.e., a large adhesive layer is ensured, whereby the stressdoes not concentrate, a release does not occur, and high reliability canbe ensured in the same manner as the V groove portion. However, asdescribed above, the end face of the optical fiber array is hardlyground precisely, and thus, the cover plate is preferably formed to besmaller than the substrate in width.

[0054] As shown in FIG. 7A that is a view illustrating a side face ofthe optical fiber array, in the case where a step 3 a is provided at therear end of a V groove in order to reduce the concentration of thestress applied to the tip end of the optical fiber, and a cover portionmount face is provided at the rear part of the substrate by one stagelower than a V groove forming face, a large amount of adhesive 6 aexists in this step 3 a. Thus, the stress at this portion caused by theadhesive concentrates on the adhesive layer 6 between the substrate 3and the cover plate 5. In the case of such structure as well, thisconstruction is particularly effective.

[0055] Further, in FIG. 7A, although R is provided at the end at thesubstrate side of the cover plate 5, a taper or R is preferably appliedto the substrate side in this manner in order to reduce the stress moresignificantly. Namely, a large amount of adhesive thickness is madegradually closer to the adhesive thickness Y, whereby the stressconcentration can be further prevented.

[0056] With respect to this stepped portion, an optical fiber is easilydamaged by an edge of the step. In the case where a release occurs evenpartially at this portion, there is apprehension that the damage of thefiber due to the step is further accelerated by the function of stress.Thus, it is very important that this portion is prevented from arelease.

[0057] In addition, in the above embodiments, when the optical fibersare fixed by pinching them between the substrate and the cover plate,the cover plate is abutted against the optical fiber so that thethickness of the adhesive layer is equal to the height of the protrusionon the substrate of the optical fibers. However, as long as the opticalfibers securely come into contact with a V groove at two points, thecover plate may not be abutted with the optical fiber. Further, althougha plurality of V grooves are provided on the substrate, even if one Vgroove exists, an adhesive layer is formed as described above, wherebygood characteristics can be maintained.

[0058] (Advantageous Effect of the Invention)

[0059] As has been described above in detail, according to the inventionaccording to the first to fourth aspects, even under severe environment,a release hardly occurs between the optical fiber and the substrate orfixed substrate, and good characteristics can be maintained.

[0060] According to the fifth aspect of the present invention, inaddition to advantageous effect of any one of the first to fourthaspects, the width of the cover plate is different from that of thesubstrate. Thus, a meniscus-like adhesive pool portion is formed, andadhesive force increases.

[0061] According to the sixth aspect of the present invention, inaddition to advantageous effect of any one of the first to fifthaspects, the stress applied to the tip end of the optical fiber isreduced, and a release hardly occurs.

[0062] Additional advantages and modifications will readily occur tothose skilled in the art. Therefore, the invention in its broader aspectis not limited to the specific details and representative embodimentsshown and described herein. Accordingly, various modifications may bemade without departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

What is claimed is:
 1. An optical fiber array comprising a holdingmember that consists of a substrate forming a sectional V shaped housinggroove for housing an optical fiber on a top face, said optical fiberhaving an optical fiber tip end bare portion housed in said holdingmember, and filling an adhesive between the substrate and a cover plateso as to fix the optical fiber to the housing groove, wherein a distancebetween a center axis of the housing groove that is an outermost portionand an end of the substrate is 5 times or more than the radium of theoptical fiber, and a distance Y between the substrate and the coverplate is L/6≦Y≦L relevant to a distance L from a contact point betweenthe housed optical fiber and the housing grove to the cover plate.
 2. Anoptical fiber array as claimed in claim 1, wherein a height of a siteprotruding from the substrate of the optical fiber housed in the housinggroove is substantially equal to the distance Y between the substrateand the cover plate.
 3. An optical fiber array as claimed in claim 1 orclaim 2, wherein the distance Y between the substrate and the coverplate is L/4≦Y≦L.
 4. An optical fiber array as claimed in any of claims1 to 3, wherein the adhesive is epoxy-based.
 5. An optical fiber arrayas claimed in any of claims 1 to 4, wherein the width of the cover plateis different from that of the substrate.
 6. An optical fiber array asclaimed in any of claims 1 to 5, wherein a placement face for placing acover portion of optical fiber is provided at the rear part of a housinggroove forming face, and a step is provided between the housing grooveforming face and the placement face, thereby placing and housing theoptical fiber.